Polymers are commonly used in various products due to their tunable mechanical properties and ease of processing. Fire retardant polymers are polymers that are resistant to degradation at high temperatures. There is need for fire-resistant polymers in a variety of fields, including the construction of small, enclosed spaces such as skyscrapers, boats, and airplane cabins. In tight spaces, the ability to escape in the event of a fire is compromised, increasing fire risk. Fire-safe polymers also find application as adhesives in aerospace materials, insulation for electronics, and in military materials such as canvas tenting. Common polymers, however, can be highly combustible and can produce toxic gases and smoke during combustion. One common way to make polymers more resistant to combustion is to include flame retardant additives in a polymer. Flame retardant additives such as polychlorinated biphenyls and brominated flame retardants, however, can pose certain health concerns.
Six novel high-temperature tolerant phosphine oxide-containing poly(4,4′-(p-phenylene)-bis(2,6-diphenylpyridinium)) polymers P-1, P-2, P-3, P-4, P-5, and P-6 were synthesized, characterized and evaluated. They were synthesized in high yield and purity. High glass transition temperature (Tg>240° C.) and high char yield (>50% at 700° C.) were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. These ionic polymers exhibit excellent processability, thin-film forming, high-temperature resistance, fire-resistance and retardation, coating, adhesion, mechanical and tensile strength, and n-type (electron transport) properties. Incorporation of phosphine oxide and bis(phenylpyridinium) moieties in the polymer backbone leads to high glass transition temperature and fire retardant properties. The use of organic counterions allows these ionic polymers to be easily processable from a number of common organic solvents. A variety of these polymers can be synthesized by utilizing structural variants of the bispyrylium salt, phosphine oxide containing diamine, and the counterion in a combinatorial fashion. These results make them very attractive for a number of applications, including as coating and structural component materials for automobiles, aircrafts, power and propulsion systems, firefighter garments, printed circuit boards, cabinets and housings for electronic and electrical components, construction materials, mattresses, carpets, upholstery and furniture, and paper-thin coating for protecting important paper documents.
The fire retardant polymers provided herein can include pyridinium salt moieties, phosphine oxide moieties, and combinations thereof. In some cases, a fire retardant polymer provided herein can include repeating units each including at least one pyridinium salt and/or and at least one phosphine oxide moiety. In some cases, a fire retardant polymer provided herein can be a random copolymer of pyridinium salt moieties and phosphine oxide moieties. In some cases, a fire retardant polymer provided herein is substantially free of halogens.
The details of one or more embodiments are set forth in the accompanying description below. Other features and advantages will be apparent from the description, drawings, and the claims.